java设计模式之职责链模式（二）

职责链模式的一个变种如下，执行某一个handler，用当前handler是否执行成功判断是否要执行下一个handler，

首先我们定义一个抽象handler类，如果当前handler执行不成功，且还有下一个handler，则继续往下执行

public abstract class Handler {
    protected Handler nextHandler;

    public void setNextHandler(Handler nextHandler) {
        this.nextHandler = nextHandler;
    }

    public final void handle(String request) {
        boolean b = doHandle(request);
        if (!b && this.nextHandler != null) {
            nextHandler.handle(request);
        }
    }

    protected abstract boolean doHandle(String request);
}

下面实现借助之前解析时间字符串的案例，写三个handler实现类

public class HandlerA extends Handler{
    @Override
    protected boolean doHandle(String request) {
        try {
            LocalDate parse = LocalDate.parse(request);
            System.out.println("HandlerA");
            System.out.println(parse);
            return true;
        } catch (Exception e) {
            System.err.println(e.getMessage());;
        }
        return false;
    }
}


public class HandlerB extends Handler {

    @Override
    protected boolean doHandle(String request) {
        try {
            LocalDateTime parse = LocalDateTime.parse(request);
            System.out.println("HandlerB");
            System.out.println(parse);
            return true;
        } catch (Exception e) {
            System.err.println(e.getMessage());
        }
        return false;
    }
}

public class HandlerC extends Handler {
    public static final DateTimeFormatter dtFormat = DateTimeFormatter.ofPattern("yyyy年MM月dd日");

    @Override
    protected boolean doHandle(String request) {
        try {
            TemporalAccessor parse = dtFormat.parse(request);
            System.out.println("HandlerC");
            System.out.println(parse);
            return true;
        } catch (DateTimeParseException e) {
            System.err.println(e.getMessage());
        }
        return false;
    }
}

我们定义一个入口函数

public class App {

    public static void main(String[] args) {
        Handler handler1 = new HandlerA();
        Handler handler2 = new HandlerB();
        Handler handler3 = new HandlerC();
        handler1.setNextHandler(handler2);
        handler2.setNextHandler(handler3);
        String d1="2022-08-08";
        String d2="2022-08-08T10:09:09";
        String d3="2022年08月08日";
        handler1.handle(d3);

    }
}

前面两个handler失败了，最后一个成功了，结果如下

输出：

Text '2022年08月08日' could not be parsed at index 4
Text '2022年08月08日' could not be parsed at index 4
HandlerC
{},ISO resolved to 2022-08-08